Core Case of the Month: November 2015

The Case

CC

Shortness of breath two hours after arthroscopy

HPI

75 yo F presents with shortness of breath 2 hours after arthroscopy. Patient states she had an outpatient arthroscopy of R shoulder that was uneventful but felt short of breath at discharge, about 30 min post-procedure, that is now progressively worsening. Denies chest pain, fevers/chills, cough, nausea/vomiting.

What is the best management of this patient?

The management of unintentional phrenic nerve block is largely supportive. Patients should also be reassured that their respiratory distress will resolve when the block wears off, which can be up to 18 hours depending on anesthetic used. Support the patient’s breathing with supplemental oxygen; for some patients this may be enough. If the patient continues to be in respiratory distress, they may require non-invasive mechanical ventilation or even intubation. In our patient, her symptoms rapidly resolved with supplemental oxygen via facemask. She was admitted to the step-down unit for observation with complete resolution of hemidiaphragmatic paralysis overnight and discharged the next day.

More Info

Interscalene block and its complications

The interscalene block is a popular brachial plexus block used for shoulder arthroscopies. It can often prevent the use of general anesthesia as well as provide post-operative pain management. Analgesia with the interscalene block will be sustained for 8-10 hours and up to 18 hours depending on the type of local anesthetic used2.

The brachial plexus courses out of the cervical spine into the upper extremities. Going from proximal to distal, the brachial plexus divides into roots (comprised of the individual nerve roots rising from the cervical spine), trunks, divisions, cords and branches. Roots of the brachial plexus form 3 trunks, the superior, middle, and inferior trunks, which traverse between the anterior and middle scalene muscles in the neck. The interscalene block is performed at the level of the C6 vertebral body, which is the same level as the cricoid cartilage. Anesthesia injected into the interscalene groove aims to block nerves C5 to C7 or the superior and middle trunks that innervate the muscles of the shoulder. The inferior trunk, C8 and T1, is less reliably anesthetized. Therefore, any procedure below the elbow may require further regional anesthesia.

There are several important structures around the interscalene space that may cause unintended complications to this block. First, as the presented patient experienced, there is almost 100% incidence of ispilateral phrenic nerve block with interscalene blocks8. The phrenic nerve (composed of contributions from C3 to C5) lies on the ventral aspect of the anterior scalene muscle (blue dot on ASM). Anterior spread of local anesthetic is rarely avoidable. Therefore, ipsilateral hemidiaphragmatic paralysis is common in patients receiving interscalene block. Phrenic nerve blocks resulting in hemidiaphragm paralysis can cause significant reduction in pulmonary function. Urmey et al found a 27% decrease in forced vital capacity, 26.4% decreased in forced expiratory volume, 15.4% decrease in peak expiratory flow rate associated with hemidiaphragmatic paralysis7. While most healthy adults would be able to tolerate hemidiaphragmatic paralysis without symptoms, patients with less pulmonary reserve such as the elderly may experience respiratory distress. It is important to consider the patient population when performing interscalene blocks as patients such as the elderly, the morbidly obese, or patients with underlying lung disease e.g. COPD may not be able to tolerate the decrease in pulmonary function.

Other lesser-associated potential complications from interscalene blocks include seizure, ipsilateral horner’s syndrome and hoarseness of voice. The carotid artery is just medial to the anterior scalene muscle. If the carotid artery is inadvertently punctured and anesthesia is introduced into the artery, seizures can occur. To suppress seizures, benzodiazepines are preferred4. Just posterior to the carotid artery resides the stellate ganglion, part of the cervical sympathetic chain. Posterior and medial migration of anesthesia can affect the stellate ganglion causing reversible horner’s syndrome (ipsilateral miosis, anhidrosis and ptosis) in about 18% of patients1. Patients with horner’s syndrome after interscalene block only require reassurance that symptoms will resolve after local anesthesia is metabolize. Of a more serious, but less common occurrence is the blockage of the recurrent laryngeal nerve which courses its way upwards around C7. Blockage of the recurrent laryngeal nerve can cause transient hoarseness, but can also cause respiratory distress if patient has underlying contralateral vocal cord disease6.

by Di Coneybeare, MD

Di was raised in Portlandia, then transplanted to New York for medical school and now residency. She enjoys exploring the city especially the food scene, playing with her dogs and seeking out green spaces. Her academic interests include ultrasound and education.

3 Comments

1) Paralysis of the hemidiaphragm
2) Complication of regional anesthesia (brachial plexus block) – nervus phrenicus block
3) Since the pathophysiology in the lungs is shunting, oxygen therapy might not be enough, leading to ventilator support until effects of local anesthethics wear off?

Interscene block is the likely regional anesthesia used for the shoulder arthroplasty. The phrenic nerve passes near brachial plexus at target for ISB so some degree of hemiparalysis of diaphragm is expected but usually not clinically significant. I question if this patient has in diagnosed lung or CV disease? Treatment start with positioning seated or recumbent > supine with supplemental O2. If still in distress perhaps mechanical ventilation as above mentioned?